1. Field of the Invention
The present invention relates to a method of accessing a storage unit having a plurality of storage portions that are, for example, magnetic disk units.
2. Description of the Related Art
A storage unit that distributively writes data blocks of a plurality of data sequences to a plurality of storage portions, and that successively reads the data blocks of the data sequences from the storage portions, is known. However, an effective accessing method for such a storage unit has been desired.
FIG. 1 is a schematic diagram showing an example of a conventional storage unit. The storage unit has seven disk units DSK 1 to DSK 7. In FIG. 1, title 1-1, title 1-2, title 1-3, . . . and so forth represent divided data blocks of a data sequence title 1. Likewise, title 2-1, title 2-2, title 2-3, . . . , title 7-1, title 7-2, . . . and so forth represent divided data blocks of data sequences title 2 to title 7. These data blocks are distributively written to the magnetic disk units DSK 1 to DSK 7. The method for distributively storing data blocks to a plurality of storage portions such as magnetic disk units is referred to as a striping method.
When the data sequence title 1 is designated and read, the data blocks title 1-1, title 1-2, title 1-3, and so forth are successively read from the magnetic disk units DSK 1, DSK 2, DSK 3, and so forth, respectively. In other words, the magnetic disk units are accessed in the order of DSK 1, DSK 2, DSK 3, DSK 4, DSK 5, DSK 6, DSK 7, DSK 1, and so forth. When a data sequence title 6 is designated and read, the magnetic disk units are accessed in the order of DSK 6, DSK 7, DSK 1, DSK 2, DSK 3, DSK 4, DSK 5, DSK 6, DSK 7, and so forth in such a manner that this access operation does not interfere with the other data access operation for the data blocks title 1-6, title 1-7, and so forth.
For example, assume that a data sequence is video data, that a data block is composed of one frame or several frames, and that a title 2 is designated. In this case, the first data block is read from the magnetic disk unit DSK 2 as title 2-1. The next data block is read from the magnetic disk unit DSK 3 as title 2-2. On the other hand, the receive and playback side buffers the data blocks so as to restore the original sequence of the video data. Alternatively, video data can be compressed corresponding to a standardized compression encoding method such as MPEG (Moving Picture Experts Group) and distributively stored as data blocks, each of which is composed of one frame or several frames.
In the storage unit having the storage portions such as the magnetic disk units DSK 1 to DSK 7, when a data sequence is distributively stored thereto and then the beginning to the end of the data sequence are successively read therefrom, the data blocks can be successively read from the magnetic disk unit DSK 1 to DSK 7 in such a process. However, for example, an order changing operation of a data sequence (for example, a fast forward operation or a rewind operation of moving picture data) or an access changing request for accessing another data sequence cannot be quickly performed.